This invention relates generally to an ultrasonic gas measuring device for detecting and determining the concentration of oxygen within a binary oxygen gas mixture. The concentration of oxygen within a binary gas mixture is then used in therapeutic medicinal applications. The invention incorporates a means for providing a more efficient and precise determination of the concentration of oxygen within a binary gas mixture, such as an oxygen/nitrogen mixture.
In the past, the analysis of simpler gas mixtures normally required the use of measurement techniques which involved difficult calibration procedures, replenishment of reagent chemicals, and/or other awkward, costly or time-consuming procedures.
Prior art devices have been developed to continuously monitor the ratio of two known gases within a gas mixture. A typical example of a binary gas composition to be measured would include oxygen/nitrogen mixtures used in the therapeutic administration of oxygen from oxygen concentrators in home health care environments. Additionally, respirators, ventilators, and air/oxygen blenders are commonly used in hospitals requiring known ranges of oxygen concentration. Gas concentration detection devices are also used in medical applications involving the application of anesthesia to individuals. In the medical field, many patients require supplemental oxygen. The two most common forms for the supply of oxygen include bottled oxygen compressed and confined within a canister, and oxygen concentrators which convert room air into oxygen. Many states require oxygen concentrators to include oxygen monitors installed to verify the concentration levels for the supply of therapeutic oxygen. Oxygen concentrator suppliers may therefore use oxygen monitors to verify correct operation, and reduce the need for maintenance of oxygen detection devices.
Prior art oxygen measurement devices are extremely sensitive to changes in temperature and are generally poorly temperature compensated. In addition, these devices are extremely sensitive to barometric pressure or humidity changes. Acoustical techniques have been used for gas analysis for measurement of the concentration of a particular gas within a binary gas mixture. The use of acoustical techniques creates severe technical problems with respect to the analysis of gases, due to the mechanical, electronic, and thermal problems associated with standing waves, temperature variations, and barometric pressure or humidity variances. The temperature of the gas must be measured and used to compensate for an accurate output reading. As the temperature increases, the sound waves within the transducer chamber travel at a faster rate due to the increased speed of the molecules of gas moving within the chamber.
Continuous wave systems have been considered appealing, due to the ability of such systems to use a resonant transmitter and receiver element which affords an adequate signal-to-noise ratio, acceptable sensitivity, and simplicity of design for a gas concentration measurement device. However, the continuous-wave approach is not free from problems, particularly with respect to standing waves within the closed transducer chamber. In a continuous-wave system, the receiver accepts acoustic energy from the transmitter within a transducer chamber and generates a signal, with a phase shift, which is affected by the mean molecular weight and temperature of the gas to be detected. The acoustical waves within the transducer chamber reflect from various surfaces, thus setting up standing waves that frustrate repeatability measurements. In addition, upon excitation of the transmitted energy, the receiver retransmits a signal at its anti-resonant frequency, in a complex fashion, back toward the transmitter. As a result, a beat frequency is encountered which yields unpredictable effects in response to temperature variations. The primary problem of gas-sensing devices, as known, is the standing waves which are encountered within the transducer chamber yielding unacceptable high signal-to-noise ratios and/or signal frequency errors.
The disclosed invention provides a more precise analysis of the concentration of a gas or gases within a gaseous mixture, primarily through the elimination of reflected standing waves within a transducer chamber. The invention thereby furnishes a more consistent and accurate analysis of the specific concentration of any one of the gases being detected, particularly oxygen, than can be achieved through the usage of the individual or combined prior art teachings.
An example of the prior art teachings include the U.S. Pat. No. 5,060,506 to Douglas and the U.S. Pat. No. 5,060,514 issued to Aylsworth. Both patents generally disclose ultrasonic gas measuring devices for the measurement of gas mixtures involving a transducer chamber having a design which does not minimize signal-to-noise ratios resulting from standing waves.